Polymers comprising alkali-insoluble core/alkali-soluble shell and copositions thereof

Abstract

Disclosed herein are core-shell polymers having an alkali-insoluble, emulsion polymer core and an alkali-soluble, emulsion polymer shell attached or associated with said core so that upon dissolving said shell with alkali, a portion of said shell remains attached or associated with said core. Also disclosed are compositions wherein said shell polymer has been neutralized and substantially, but not totally, dissolved so as to form a blend of neutralized core-shell polymer and an aqueous solution of neutralized shell polymer.

We claim: 
     
       1. A composition comprising a core-shell polymer having an alkali-insoluble, emulsion polymer core and an alkali-soluble, emulsion polymer shell attached or associated with said core so that upon dissolving said shell with alkali, a portion of said shell remains attached or associated with said core, wherein the weight ratio of core polymer to shell polymer is about 99:1 to about 1:99 and said core and shell are each independently polymerized from monomer systems comprised of monomers selected from the group consisting of methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, decyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, acrylonitrile, acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, styrene, substituted styrene, vinyl acetate, and other C 1  to C 12  alkyl acrylates. 
     
     
       2. The composition of claim 1 wherein the weight average molecular weight, as determined by gel permeation chromatography, of said shell polymer is about 5,000 to about 50,000 and said core polymer is greater than about 50,000. 
     
     
       3. The composition of claim 1 wherein the T g  of said core polymer is about -20° C. to about 30° C. 
     
     
       4. The composition of claim 1 wherein said core polymer is polymerized first to a particle size of about 60 to 140 nm. 
     
     
       5. The composition of claim 1 wherein said core polymer is polymerized second, and due to the hydrophobicity of the core polymer, it becomes a domain within the particles of the alkali-soluble shell polymer. 
     
     
       6. The composition of claim 1 wherein said shell polymer has a T g  of at least about 100° C. 
     
     
       7. The composition of claim 1 wherein said shell polymer is polymerized from a mixture of unsaturated monomers comprising about 10% to about 60% by weight acid-containing unsaturated monomer and said core polymer is polymerized from a monomer mixture comprising less than about 3% by weight acid-containing unsaturated monomer. 
     
     
       8. The composition of claim 7 wherein said shell is polymerized from a monomer mixture comprising about 20 to 50% methacrylic acid and said core is polymerized from a monomer mixture comprising about 0.01% to about 1.5% methacrylic acid. 
     
     
       9. The composition of claim 8 wherein said core polymer is polymerized from a monomer mixture containing about 0.3% to about 0.7% by weight methacrylic acid. 
     
     
       10. The composition of claim 1 wherein said shell polymer has been neutralized and substantially, but not totally, dissolved so as to form a blend of neutralized core-shell polymer and an aqueous solution of neutralized shell polymer. 
     
     
       11. The composition of claim 10 wherein said shell polymer is dissolved with a base selected from the group consisting of ammonia, triethylamine, monoethanolamine and dimethylaminoethanol. 
     
     
       12. The composition of claim 1 wherein said core is polymerized from a monomer mixture free of carboxylic acid. 
     
     
       13. The composition of claim 1 wherein the weight ratio of core polymer to shell polymer is about 80:20 to about 20:80. 
     
     
       14. The composition of claim 1 wherein the weight ratio of core polymer to shell polymer is about 65:35 to 35:65. 
     
     
       15. The composition of claim 1 wherein the weight ratio of core polymer to shell polymer is about 60:40 to about 40:60. 
     
     
       16. Process for preparing the composition of claim 1 wherein the core polymer and shell polymer are sequentially polymerized. 
     
     
       17. Process comprising applying the composition of claim 10 to a substrate as a heat-resistant clear overprint varnish. 
     
     
       18. A hydraulic cement composition containing the core-shell polymer of claim 1. 
     
     
       19. A process for modifying cement comprising incorporating therein the core-shell polymer of claim 1. 
     
     
       20. A process of claim 19 wherein said core-shell polymer has been spray-dried to give free-flowing, dried particles. 
     
     
       21. An ink or paint composition containing the core-shell polymer of claim 1, a pigment and a dispersing agent. 
     
     
       22. A paint composition of claim 21 containing at least one, wetting agent, rheology modifier, coalescent, base and drying retarder.